1. Field of the Invention
The present invention relates to a ultraviolet electroluminescent element and a laser luminescent element capable of emitting in ultraviolet range.
2. Description of Related Art
Electroluminesce (hereinafter referred to as "EL") which is generated by the application of a strong electric field to a fluorescence body has two types. One type is a current injection type EL, such as a light emitting diode. The other is a voltage excitation type EL. As voltage excitation type EL, a dispersion powder type EL panel in which material obtained by dispersing fine fluorescence powder into a synthetic resin or a glass powder is disposed between a transparent electrode and a back electrode, and a double insulation film EL panel in which a film-shaped fluorescent body emitting layer, made by vacuum evaporation or spattering method is completely covered by a dielectric insulating layer, is disposed between a transparent electrode and a back electrode are known. The emitting color of a voltage excitation type EL element varies with fluorescent material. A fluorescent material obtained by adding 0.3 to 0.5 weight percents of manganese to zinc sulfide (ZnS:Mn) provides yellow-orange color; SrS:Ce blue color, CaS:Ce or CaS:Er green color; and CaS:Eu red color. Fluorescent material ZnS:TmF.sub.3 provides blue color; ZnS:TbF.sub.3 green color; and ZnS:SmF.sub.3 orange-red color.
In recent years, an injection type EL element with two layers of a hole transporting layer and an emitting layer has been highlighted. FIG. 11 shows a cross-section of the two-layer EL element in which a hole transporting layer 93 and an emitting layer 94 are mounted on a transparent electrode (ITO) 92, formed on a glass baseplate 91, and an upper electrode 95 is formed thereon. Aromatic diamine derivative or polymethyl phenylsilane is used for the hole transporting layer 93, and 8-hydroxy quinoline aluminum (Alq.sub.3), an emitting metal complex, is used for the emitting layer 94. The upper electrode 95 is an electrode in which Mn and Ag are laminated. The hole transporting layer 93 transports holes and blocks electrons, which prevents the electrons from being transported to the electrode without rebonding with the holes.
When the EL element shown in FIG. 11 is operated in continuous direct current mode under the condition of positive ITO and forward bias, a bright green emission color is generated. FIG. 12 shows the emitting spectrum of the EL element and Alq.sub.3. In this figure, a solid line shows the spectrum of the EL element and a dotted line shows the spectrum of Alq.sub.3. The spectrum of the EL element coincides with that of Alq.sub.3, so that the EL is from Alq.sub.3 [Polymer Preprints, Japan, 40(3), 1071(1991); Applied Physics Letter, 59(21), 2760].
In a paper "Polymer Preprints" [Polymer Preprints, Japan, 44(3), 325 (1995)] is stated that polysilane with oxygen bridge formation structure emits in an electrical field. According to the paper, polymethyl phenylsilane (PMPS) is painted on an ITO base plate and is bridged under heat, and then single-layer EL element with ITO/bridged PMPS/Al structure to which Al is evaporated emits in the electrical field with emission energy center of 1.8 eV. It is stated, in this paper, that normal polysilane without oxygen bridge formation structure does not emit.